1. Technical Field
The present invention generally relates to lubricating oil compositions.
2. Description of the Related Art
Metal salts of sulfurized alkylphenols are useful lubricating oil additives which impart detergency and dispersancy properties to the lubricating oil composition as well as providing for an alkalinity reserve in the oil. Alkalinity reserve is necessary in order to neutralize acids generated during engine operation. Without this alkalinity reserve, the acids so generated would result in harmful engine corrosion.
U.S. Patent Application Publication No. 20080070818 (“the '818 publication”) discloses a lubricating oil composition including at least one sulphurized overbased metal phenate detergent prepared from a C9-C15 alkyl phenol, at least one sulphurizing agent, at least one metal and at least one overbasing agent; the detergent including less than 6.0% by combined mass of unsulphurized C9-C15 alkyl phenol and unsulphurized metal salts thereof. Examples A and B disclosed in the '818 publication obtained an overbased detergent having 5.58 and 3.84 mass %, respectively, of unsuphurized alkyl phenol and its unsulphurized calcium salt.
Accordingly, it would be desirable to provide an improved process for making metal salts of sulfurized alkylphenols which have relatively low level of unreacted starting alkylphenol.